1. Field of the invention
The present invention relates, in general, to electrical conductors, and, more specifically, to shielded electrical power supply cables.
2. Description of the Art
Internal electrical wiring in residential homes for 15 ampere A.C. power supply electrical service has for years been standardized as 14-2G type NM-B sheathed cable. This sheathed cable consists of three 14 gage solid conductors, with the line and neutral conductors individually insulated and disposed in a parallel flat lay on opposite sides of an insulated ground conductor. This cable construction has several features which minimize magnetic field interaction and damping of mechanical vibrations generated by the 60 Hz North America electrical power carrier frequency. Such features include the spacing apart of the current carrying line and the neutral conductors, the use of relatively stiff, solid 14 AWG conductors, and relatively stiff insulation and cable jacket. These features combine to resist the repelling forces caused by the magnetic fields associated with the two closely spaced line and neutral conductors.
Conversely, typical A.C. power supply cords for electrical appliances, such as audio amplifiers, preamplifiers, etc., have a construction which is optimized for maximum flexibility and durability in potentially high flex cycle applications. Such power supply cords have close conductor spacing geometry which increases magnetic interaction between the line and neutral current carrying conductors. Such cords also typically use stranded conductors and soft fillers, such as cotton and paper, between the conductors and the outer jacket material. All of these features compromise the self-damping quality of the power supply cord thereby leading to increased vibration of the individual conductors due to the interacting magnetic fields generated by the current carrying conductors. The movement of the conductors due to magnetic field interaction is also enhanced by the use of the soft fillers and the relatively flexible outer jacket.
Thus, it would be desirable to provide a power supply cable, particularly suited for use in supplying electrical power to audio equipment, which has reduced vibration of the individual current carrying conductors, has a reduced inductance, has a solidly filled construction to minimize any movement of the individual conducts within the cable, and has a line and neutral conductor arrangement which minimizes magnetic field interaction between the line and neutral conductors within the cable.